Apparatus and method for penetrating cement surrounding a tubular

ABSTRACT

Apparatus and method for penetrating cement ( 300 ) surrounding a tubular ( 200 ) cemented to a formation ( 400 ). The apparatus comprises a bore ( 10 ) through the tubular wall ( 200 ), and an intermediate fluid channel ( 102 ) in an insert ( 100 ) within the bore. An inner sleeve ( 120 ) may be disposed on the interior surface of the tubular wall ( 200 ). The inner sleeve ( 120 ) is movable between a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, and an open position wherein fluid connection between the interior of the tubular and the bore is allowed. An abrasive and/or etching fluid is supplied through the channel ( 102 ) to remove cement and/or the insert ( 100 ) or piston assembly.

The present invention relates to an apparatus and a method for penetrating cement surrounding a tubular.

BACKGROUND

A well extending through geological formations may be used for exploration and production of oil and/or gas, water production and/or in geothermal applications. Building a well typically involves drilling a borehole, inserting a steel casing into the wellbore and cementing the casing to the formation. The casing provides structural stability, for example by preventing weak rock or sand from caving into the borehole. When the cement is set, the next section is drilled through the formation in the extension of the existing casing. A liner is then hung off of the casing, and cemented to the formation. This process can be repeated until the well has reached the desired depth. A well may also comprise sections of uncased or open borehole, sections of casing or lining with sand screens, sections surrounded by gravel packs etc, as is well known in the art. However, for the purposes of the following disclosure, only wellbores with a tubular steel lining cemented to the formation are considered. Further, a casing and a liner will be collectively referred to as a tubular in the following description and accompanying claims. In other words, no distinction will be made between a casing and a liner in the following.

In order to allow fluid flow from the formation into the wellbore, the steel tubular and cement must be penetrated at depths corresponding to a layer containing oil and/or gas, an aquifer or the like, hereinafter referred to as a production zone. Conventionally, the perforation has been performed by using an explosive charge in a device known as a perforation gun. However, explosives require special handling according to strict safety rules, they may damage the formation and they have other disadvantages. Hence, there is a tendency to avoid explosives whenever possible.

Any time after penetration, i.e. when a fluid path is established between the formation and the interior of the well bore, the production zone may be ‘stimulated’ in order to facilitate the fluid flow. Techniques for stimulating a zone involve hydraulic fracturing, in which hydraulic pressure is applied to force open cracks in the rock and insert sand or other granular material into the cracks. When the fracturing pressure is removed, the granular material remains in the cracks and keeps them open. Known stimulation techniques also include injection of acid, solvents, surfactants etc in order to reduce the viscosity of the production fluid or the adhesion of production fluid to the surrounding rock.

The purpose of the present invention is to overcome the problems of prior art, while keeping the benefits of well known techniques and equipment, in particular to penetrate the cement surrounding a tubular cemented to a formation without using explosives.

SUMMARY OF THE INVENTION

According to the present invention, in a first aspect, this is accomplished by an apparatus for penetrating cement surrounding a tubular cemented to a formation, the apparatus comprising a bore through the tubular wall and an intermediate fluid channel disposed within an insert within the bore. In an embodiment, an inner sleeve may be disposed on the interior surface of the tubular wall, the inner sleeve being movable between a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, and an open position wherein fluid connection between the interior of the tubular and the bore is allowed. The bore through the tubular wall (200) may be provided in a direction perpendicular to the tubular wall.

In one embodiment, the insert is a piston assembly movably disposed in the bore, the piston assembly comprising a hardened tip at an outer end and a piston at an inner end, and the fluid channel being provided from the piston to the vicinity of the tip. In a further embodiment, the apparatus comprises a substance capable of swelling when a liquid is added thereto, the swelling substance being disposed between the piston and an interior wall, and the interior wall comprising ports that are opened or closed by the inner sleeve.

In another aspect, the invention concerns a method for penetrating cement surrounding a tubular cemented to a formation, the method comprising the steps of: providing a fluid from an interior of the tubular through an intermediate fluid channel, the fluid being capable of removing cement and/or material from an insert surrounding the fluid channel.

One embodiment of the method further comprises the step of forcing a hardened tip from the tubular wall into the cement with sufficient force to cause a groove and/or cracks in the cement before providing the fluid. The groove and/or cracks provide a larger area of attack for the fluid. Forcing the hardened tip into the cementing may involve applying hydraulic pressure from the interior of the tubular on a piston rigidly connected to the tip. Forcing the hardened tip into the cementing may also involve opening a fluid channel from the interior of the tubular to an expandable substance arranged to exert a force on the piston. Providing the fluid may involve providing an abrasive fluid or providing at least one chemical capable of etching cement and/or the material of the insert.

In an embodiment, the method further comprises prior to providing the fluid, providing an inner sleeve on an interior surface of the tubular wall, and moving the inner sleeve from a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, to an open position wherein fluid connection between the interior of the tubular and the bore is allowed.

Further embodiments and advantages of the invention will be apparent from the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the followings drawings, where:

FIG. 1 is a schematic cross sectional view of an embodiment of the invention;

FIG. 2 is a schematic cross sectional view of a further embodiment of the invention;

FIG. 3 is a schematic cross sectional view of an alternative embodiment of the invention;

DETAILED DESCRIPTION

The drawings are schematic and intended to illustrate the principles of the present invention. Hence, the figures are not to scale, and a number of details are omitted for the sake of clarity.

FIG. 1 illustrates an embodiment of an apparatus to penetrate the cement 300 surrounding a tubular (200) cemented to a formation (400). A bore 10 extends through the tubular wall 200. In FIG. 1 the bore extends through the tubular wall 200 in a direction perpendicular to the wall, i.e. radially with respect to the tubular. However, the bore 10 may also extend through the tubular wall 200 in a sloping direction. The bore is provided with a removable seal (140) near an exterior surface of the tubular.

An intermediate fluid channel 102 within an insert 100 essentially provides a fluid path through the wall of the tubular. However, the diameter of the intermediate fluid channel is considerably less than the diameter of the bore. This may be useful in applications where a number of ports are to be opened, e.g. by a drop ball, and a small pressure difference is desired over each port corresponding to the bore 10. Later, an abrasive fluid, for example slurry for hydraulic fracturing, can abrade the insert in order to fully open the port or bore. In such an application, the bore could be lined 101 with a hard material, e.g. tungsten carbide (WC), ceramic material or hardened steel, and the insert would be manufactured form a softer material, for example a softer steel or other metal e.g. aluminium. This method can also be used to penetrate the cement around the casing as illustrated in FIG. 1.

An inner sleeve 120 is disposed on the interior surface of the tubular wall 200. The inner sleeve is movable between a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, and an open position wherein fluid connection between the interior of the tubular and the bore is allowed. The sleeve is provided to close the bore during run in, and may be rotated around, or alternatively displaced axially along, the axis of rotation of the tubular. In both cases, at least one opening in the inner sleeve is aligned with the bore in the open position, and not aligned in the closed, or run-in, position shown in the FIGS. 1-3.

FIG. 2 illustrates a preferred embodiment of the apparatus, wherein the insert 100 is a piston assembly disposed in the bore 10. The bore is provided with a removable seal (140) near an exterior surface of the tubular. The piston assembly can be displaced in the axial direction of the bore 10, which corresponds to the radial direction of the tubular. When the inner sleeve 120 is moved to its open position, hydraulic pressure may work in the interior surface of the piston 110, i.e. to the left on FIG. 2. It is readily seen that the pressure and piston area can be adapted such that the piston assembly is forced radially outwards with respect to the tubular, i.e. towards the right hand side of FIG. 2, such that the hardened tip 105 penetrates the seal 140 and enters a distance into the cement 300.

To achieve this, the piston assembly comprises a hardened tip 105 at an outer end rigidly connected to a piston 110 at an inner end of the bore. The tip can be made of a ceramic material, as ceramics tend to withstand compression forces quite well even if they are brittle and break easily when subjected to tensile forces. Alternatively, the tip 105 can be made of hardened steel or another suitable material. The tip is sufficiently hard to penetrate a distance into the cement and provide a groove and/or cracks. Typical compressive strength of the cement is from about 3000 psi and above, and the tip is forced into the cement with sufficient force in order for the pressure against the cement under the tip to become larger than the compressive strength. The enlarged surface of the groove and/or cracks provides an area of attack for an etchant or abrasive fluid as described below. This fluid is supplied from the interior of the tubular (to the left on FIGS. 1-3) through the fluid channel(s) 102, which are provided through the piston assembly to the vicinity of the tip 105.

The seal 140 in the FIGS. 1-3 is intended to protect the bore during run in. It can be provided as a lid as illustrated. Alternatively, the seal 140 can be a portion of the tubular wall 200 with reduced thickness, or a plug made from a suitable material such as a plastic or resin. In particular, the tip 105 in FIGS. 2 and 3 should penetrate seal 140 without requiring too much force, so the seal 140 should just be able to withstand the forces it may encounter during run-in.

FIG. 3 resembles FIG. 2 in that it comprises a piston assembly within a housing. In FIG. 3, however, a swelling substance 150 is disposed between the piston 110 and an interior wall 103. The interior wall 103 is provided in the bore 10 facing the inner sleeve 120. The interior wall 103 has ports or fluid channels 102 as discussed above. The ports 102 may be opened by the inner sleeve 120, such that liquid can be supplied to the swelling material. When liquid is supplied, the swelling material will exert equal forces in opposite directions on the interior wall 103 and the piston 110. Hence, the interior wall 103 must be able to withstand the forces required to drive the tip 105 into the cement 300.

In all of the embodiments above, a fluid is provided from the interior of the tubular through an intermediate fluid channel 102. The fluid must be capable of removing cement and/or material from an insert surrounding the fluid channel. A slurry containing sand or ceramic particles, such as a slurry used for hydraulic fracturing, is known to abrade metal inserts and cement. The amount of abraded material is proportional to the area in which the abrasive fluid is allowed to work. Hence, a small groove tends to be enlarged by the abrasion. Similarly, cracked cement tends to be abraded more easily than solid cement. Alternatively, the fluid may be corrosive or etching. For example, it is well known that NaOH etches aluminium, and hence could be used to remove aluminium inserts. Similarly, HCI could be used for etching the cement 300 and/or stimulate a limestone formation. Obviously, different fluids could be used at separate times. The choice of suitable materials and chemicals are known in the art, and hence left to the skilled person.

While the invention has been described with reference to certain embodiments, the scope of the invention is defined by the following claims. 

1. Apparatus for penetrating cement (300) surrounding a tubular (200) cemented to a formation (400), the apparatus being characterized by: a bore (10) through the tubular wall (200), and an intermediate fluid channel (102) in an insert (100) within the bore.
 2. Apparatus according to claim 1, further comprising: an inner sleeve (120) disposed on an interior surface of the tubular wall (200), the inner sleeve being movable between a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, and an open position wherein fluid connection between the interior of the tubular and the bore is allowed.
 3. Apparatus according to claim 1, wherein the bore (10) through the tubular wall (200) is in a direction perpendicular to the tubular wall (200).
 4. Apparatus according to claim 1, wherein the insert (100) is a piston assembly disposed in the bore and movable in an axial direction of the bore (10), the piston assembly comprising a hardened tip (105) at an outer end and a piston (110) at an inner end, and the fluid channel (102) being provided through the piston assembly to the vicinity of the tip (105).
 5. Apparatus according to claim 1, wherein the bore is provided with a removable seal (140) near an exterior surface of the tubular.
 6. Apparatus according to claim 1, wherein the insert (100) within the bore (10) is erodible by an abrasive and/or etching fluid.
 7. Apparatus according to claim 1, wherein the insert is disposed in a housing (101) made from a material that is more resistant to abrasion and/or corrosion than the material of the tubular wall (200).
 8. Apparatus according to claim 4, further comprising a substance (150) capable of swelling when a liquid is added thereto, the swelling substance (150) being disposed between the piston (110) and an interior wall (103), and the interior wall (103) comprising ports (102) that are opened or closed by the inner sleeve (120).
 9. Method for penetrating cement (300) surrounding a tubular (200) cemented to a formation (400), the method being characterized by: providing a fluid from an interior of the tubular through an intermediate fluid channel (102), the fluid being capable of removing cement and/or material from an insert (100) surrounding the fluid channel.
 10. Method according to claim 9, further comprising prior to providing the fluid, providing an inner sleeve (120) on an interior surface of the tubular wall (200), and moving the inner sleeve from a closed position wherein fluid connection between the interior of the tubular and the bore is prevented, to an open position wherein fluid connection between the interior of the tubular and the bore is allowed.
 11. Method according to claim 9, further comprising the step of forcing a hardened tip (105) from the interior of the tubular wall (200) into the cement with sufficient force to cause a groove and/or cracks in the cement before providing the fluid.
 12. Method according to claim 11, wherein forcing the hardened tip (105) into the cementing involves applying hydraulic pressure from the interior of the tubular on a piston (110) rigidly connected to the tip (105).
 13. Method according to claim 11, wherein forcing the hardened tip into the cementing involves opening a fluid channel from the interior of the tubular to an expandable substance arranged to exert a force on the piston (110).
 14. Method according to claim 9, wherein providing the fluid involves providing an abrasive fluid.
 15. Method according to claim 9, wherein providing the fluid involves providing at least one chemical capable of etching cement and/or the material of the insert. 